Method of processing signals for optical disc device and optical disc device utilizing two split photo detectors

ABSTRACT

An object of this invention is to provide a method for processing signals for an optical disc device and an optical disc device for immediately determining the on-track state of a main beam light impinging on an optical disc including land areas on which information is recorded, said optical disc being track-formatted to have a double spiral structure. In recording or reproducing information on or from the land areas while track-controlling a first reflected light (MB) based on a second reflect light (SB 1 ) and a third reflect light (SB 2 ), the phases of a sum signal (SUM) and a difference signal (DIFF) between a first push-pull signal (PP 1 ) obtained from an output from a first split photo conductor ( 21 ) and a second push-pull signal (PP 2 ) obtained from an output from a second split photo conductor ( 23 ) are compared to determine from the mutual phase relationship which land area is providing the first reflected light (MB).

TECHNICAL FIELD

The present invention relates to a method of processing signals for anoptical disc device and the optical disc device.

BACKGROUND ART

On a recordable optical disc such as a minidisc or a CD-R that isrotated at a constant linear velocity (CLV), address informationindicating absolute positions on the optical disc and rotation controlinformation for the optical disc are recorded beforehand by usingwobbling guide grooves. The address information is encoded usingrecording codes (for example, biphase codes) that enable easy clocksynchronization during reproduction, and signals obtained byFM-modulating these recording codes are recorded on the optical disc insuch a way as to wobble through the guide grooves.

Such an optical disc is reproduced by obtaining from the optical discFM-modulated signals formed by means of wobbling through the guidegrooves, and then FM-demodulating the signals to extract biphase-encodedaddress information. Furthermore, a PLL (Phase Locked Loop) circuit isused to extract synchronizing clocks, which are then biphase-decoded todetect addresses. The rotation control information for the optical discis synchronizing clocks extracted from the biphase signals and controlsa spindle motor to rotate the optical disc so that the frequency andphase of the synchronizing clocks have predetermined values.

In such a system, efforts are being made to reduce the track pitch inorder to accommodate the increased density of information recorded on anoptical disc, but simply reducing the track pitch may cause crosstalkfrom adjacent wobbling grooves. An optical disc 5 of a track format suchas that shown in FIG. 4 is used to avoid interference by crosstalk. Theoptical disc 5 has two types of land areas 3, 4 formed in a doublespiral structure. The land areas 3 and 4 are two discontinuous areas.The land area 3 is sandwiched between a non-wobbling groove 2, which isshown to the left of the land area 3, and a wobbling groove 1, which isshown to the right of the land area 3, and information is recorded onthis area 3. The land area 4 is sandwiched between the wobbling groove 1shown to the left of the land area 4 and the non-wobbling groove 2 shownto the right of the land area 4, and as in the land area 3, informationis recorded on this area 4. The wobbling groove 1 is wobbled to providepredetermined signals including address information and rotation controlinformation (hereafter referred to as “wobble information”), while thenon-wobbling groove 2 is not wobbled. The interval T between thewobbling grooves 1 is twice the track pitch Tp between the wobblinggroove 1 and the non-wobbling groove 2 so that the structure is unlikelyto be affected by crosstalk.

In the optical disc 5 of such a track format, the method called“differential push-pull” is used to control the tracking of a beam lightimpinging on one of the land areas 3 and 4. In this differentialpush-pull, the land area 3 is irradiated with a main beam M, and thewobbling groove 1 and the non-wobbling groove 2 are irradiated withsubbeams SB1, SB2, respectively. Reflected lights of the subbeams arereceived by split photo detectors 21, 23, as shown in FIG. 5. Detectionoutputs from the split photo detectors 21, 23 are inputted todifferential amplifiers 24, 25, respectively, to obtain differencesignals (push-pull signals PP1, PP2). The push-pull signals PP1, PP2 aredemodulated so that wobble information is obtained using one of thepush-pull signals PP1, PP2 that detects a reflected light from thewobbling groove 1. Thus, the wobble information can be detected fromeither the subbeam SB1 or SB2. For example, Japanese Patent No. 1917370describes tracking control in which, of three difference signalsobtained by means of irradiation with the main beam MB and the twosubbeams SB1, SB2, any two difference signals are calculated todetermine their difference in order to obtain a tracking error signal.

Due to their double spiral structure shown in FIG. 4, the two land areas3, 4 on which information is recorded are arranged to sandwich thewobbling groove 1. Since wobble information is recorded in the wobblinggroove 1, address (absolute position) information on the two land areas3, 4 is obtained from the shared wobbling groove 1 sandwiched by the twoland areas 3, 4. Thus, wobble information is obtained from the wobblinggroove 1 whether the main beam MB is impinging on the land area 3 or 4.

Specifically, if the main beam MB is impinging on the land area 3,wobble information is obtained by detecting a wobble signal from areflected light of the subbeam SB2, whereas if the main beam MB isimpinging on the land area 4 as shown by the dotted line, wobbleinformation is obtained by detecting a wobble signal from a reflectedlight of the subbeam SB1. Thus, by determining which of the subbeamsSB1, SB2 provides wobble information, it can be determined which of thetwo land areas 3, 4 is irradiated with the main beam MB.

This method, however, requires the two push-pull signals PP1, PP2obtained from reflected lights of the two subbeams SB1, SB2 to beconstantly demodulated by respective demodulating means. That is, two FMdemodulating circuits 29 and two biphase demodulators 30 must beprovided and constantly operated. Furthermore, FM demodulation andbiphase decoding involve processing delay time, so it cannot bedetermined whether the main beam MB is impinging on the land area 3 or4, immediately after the beam has focused on the land area.

An object of this invention is to provide a method of processing signalsfor an optical disc device and an optical disc device that canimmediately determine the on-track state of the main beam light using asimple configuration.

DISCLOSURE OF THE INVENTION

An optical disc device signal processing method according to thisinvention can compare the phases of a sum signal and a difference signalobtained by calculating a push-pull signal obtained from an output froma split photo detector for detecting a reflected light of a subbeam SB1and a second push-pull signal obtained from an output from a secondsplit photo detector for detecting a reflected light of a subbeam SB2,in order to determine from the mutual phase relationship which land areais reflecting a main beam light, thereby immediately determine theon-track state of the main beam light using a simple configuration.

In a method of processing signals for an optical device according to theinvention, in a track format optical disc has two land areas of a doublespiral structure on which information is recorded, said land areas beingarranged adjacent to each other sandwiching therebetween a wobblinggroove on which wobble information is recorded by wobbling, and hasnon-wobbling grooves arranged outside the land areas, the methodcomprising the steps of: detecting a first reflected light obtained byirradiating the land area; using a first split photo detector disposedat a first prescribed position to detect a second reflected lightobtained by irradiating the wobbling groove or the non-wobbling groovelocated adjacent to one side of the land area providing the reflectedlight; using a second split photo detector disposed at a secondprescribed position to detect a third reflected light obtained byirradiating the wobbling groove or the non-wobbling groove locatedadjacent to the other side of the land area providing the reflectedlight; and recording or reproducing information on or from the land areawhile executing tracking control based on the first, second, or thirdreflected light or on a combination of these lights, wherein phases of asum signal and a difference signal are compared between a firstpush-pull signal obtained from an output from the first split photodetector and a second push-pull signal obtained from an output from thesecond split photo detector, in order to determine from the phaserelationship obtained between said two signals which land area isproviding the first reflected light. This method can immediatelydetermine the on-track state of the main beam light without causing aprocessing delay.

In a optical disc device according to the invention, in which a trackformat optical disc has two land areas of a double spiral structure onwhich information is recorded, said land areas being arranged adjacentto each other sandwiching therebetween a wobbling groove on which wobbleinformation is recorded by wobbling, and has non-wobbling groovesarranged outside said land areas, said optical disc device executing:detecting a first reflected light obtained by irradiating the land area;using a first split photo detector disposed at a first prescribedposition to detect a second reflected light obtained by irradiating thewobbling groove or the non-wobbling groove located adjacent to one sideof the land area providing the reflected light; using a second splitphoto detector disposed at a second prescribed position to detect athird reflected light obtained by irradiating the wobbling groove or thenon-wobbling groove located adjacent to the other side of the land areaproviding the reflected light; and recording or reproducing informationon or from the land area while executing tracking control based on thefirst, second, or third reflected light or a combination of theselights. The optical disc device comprises: a signal processing means fordetecting a sum signal and a difference signal between a first push-pullsignal obtained from an output from the first split photo detector and asecond push-pull signal obtained from an output from the second splitphoto detector; and a phase comparator for comparing phases of the sumsignal and the difference signal to determine a mutual phaserelationship, in order to use a determination output from the phasecomparator as land area determination information. Thus, an optical discdevice can be obtained in order for immediately determining the on-trackstate of the main beam light using a simple configuration.

In addition, the optical disc device may demodulate an output signalfrom the signal processing means to obtain address information, wherebythe address information can be obtained using one set of demodulatingmeans.

Furthermore, the optical disc device may have a signal selector thatselects between the first and second push-pull signals based on the landarea determination information output from the phase comparator, wherebythe push-pull signal selected by the signal selector is demodulated toobtain address information.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of an address modulating circuit according toEmbodiment 1 of this invention;

FIG. 2 is a block diagram showing a configuration of an optical discdevice according to Embodiment 1;

FIG. 3 is a block diagram of an address demodulating circuit accordingto Embodiment 2 of this invention;

FIG. 4 is a schematic drawing outlining a track format of the opticaldisc; and

FIG. 5 is a block diagram of an address demodulating circuit of aconventional optical disc device.

EMBODIMENTS Embodiment 1

An optical disc device that implements an optical disc device signalprocessing method according to this invention is composed of an opticaldisc 5, an optical pickup 7, an address demodulating circuit 14, and asystem controller 15, as shown in FIG. 2.

A spindle motor 6 rotates the optical disc 5 at a predetermined speed,and the optical pickup 7 irradiates the optical disc 5 with a beam lightto detect a reflected light in order to convert it into an electricsignal. A magnetic head driver 9 drives the magnetic head 8 at apredetermined magnetic intensity, and the magnetic head 8 applies to theoptical disc 5 magnetic fields modulated using recorded data.

A semiconductor laser driver 10 allows a semiconductor laser (not shown)disposed in the optical pickup 7 to emit light at a predeterminedintensity.

Signals detected by the optical pickup 7 are supplied to a reproducedsignal processing circuit 11, a focus servo circuit 12, a tracking servocircuit 13, and an address demodulating circuit 14.

The reproduced signal processing circuit 11 is supplied with areproduced signal corresponding to recorded information recorded on theoptical disc 5. The reproduced signal processing circuit 11 processes,for example, binarizes the reproduced signal and outputs reproduced dataas digital data.

The focus servo circuit 12 obtains focus error information from thesignal supplied by the optical pickup 7 and controls the optical pickup7 according to the focus error information in order to control a beamlight to focus on the optical disc 5.

The tracking servo circuit 13 obtains a tracking error signal from thesignal supplied by the optical pickup 7 and controls the optical pickup7 according to the tracking error signal in order to control beam lighttracking so that a beam light focuses on a predetermined track.

The address demodulating circuit 14 obtains a wobbling signal from thesignal supplied by the optical pickup 7 and demodulates the wobblingsignal to obtain address information indicating which part of theoptical disc 5 is irradiated with the main beam light while obtainingrotation control information required for the spindle motor 6 to rotatethe optical disc 5 at a specified line speed.

The system controller 15 controls the optical disc device to be in arecording state or a reproduction state.

The address demodulating circuit 14 is configured by split photodetectors 21, 23, a quadrant photo detector 22, a signal processingmeans 31, a phase comparator 28, and a demodulating means, as shown inFIG. 3. The demodulating means is configured by an FM demodulator 29 anda biphase demodulator 30.

Reflected lights of subbeams SB1, SB2 impinging on a wobbling groove 1and a non-wobbling groove 2, which are shown in FIG. 4, are incident onthe split photo detector 21 acting as a first split photo detector andthe two photo detector 23 acting as a second split photo detector,respectively, which photo detectors are both disposed at prescribedpositions within the optical pickup 7 shown in FIG. 2. The reflectedlights are then converted into electric signals.

A reflected light of a main beam MB impinging on a land area 3 or 4,which is shown in FIG. 4, is incident on the quadrant photo detector 22shown in FIG. 1 and is used to detect a focus error signal.

The signal processing means 31 is configured by, for example,differential amplifiers 24, 25, an adder 29, and a subtractor 27.

Two detection outputs from the split photo detector 21 are supplied tothe differential amplifier 24 to obtain a push-pull signal differentoutput PP1 as a first push-pull signal. Likewise, two detection outputsfrom the split photo detector 23 are supplied to the differentialamplifier 25 to obtain a push-pull signal different output PP2 as asecond push-pull signal. The push-pull signals PP1, PP2 are obtainedfrom the reflected lights of the subbeams SB1, SB2, respectively. Sinceone of the subbeams SB1, SB2 is tracing the wobbling groove 1, one ofthe push-pull signals PP1, PP2 has its amplitude varied due to wobbling.

The two push-pull signals PP1, PP2 are supplied to the adder 26 and thesubtractor 27, respectively. The adder 26 adds the two push-pull signalsPP1 and PP2 together to output a sum signal SUM. The subtractor 27subtracts the push-pull signal PP2 from the push-pull signal PP1 tooutput a difference signal DIFF.

The phase comparator 28 compares the phases of the sum signal SUM withthe phase of the difference signal DIFF, and determines whether they arein same phase or out of phase by 180°.

In FIG. 4, while the main beam MB is tracing the land area 3, thesubbeam SB1 traces the non-wobbling groove 2 and the subbeam SB2 tracesthe wobbling groove 1. At this point, the push-pull signal PP2 has itsamplitude varied according to the wobbling groove 1, whereas thepush-pull signal PP1 is in a non-signal state and consists only of noisecomponents. Accordingly, the sum signal SUM shown in FIG. 1 is almostequal to the push-pull signal PP2. Likewise, the difference signal DIFFis almost equal to a signal obtained by reversing the push-pull signalPP2. Two signals out of phase by 180° are supplied to the phasecomparator 28, which then determines that the phases of these signalsare different by 180°.

In FIG. 4, while the main beam MB is tracing the land area 4, thesubbeam SB1 traces the wobbling groove 1 and the subbeam SB2 traces thenon-wobbling groove 2. At this time, the push-pull signal PP1 has itsamplitude varied according to the wobbling groove 1, whereas thepush-pull signal PP2 is in a non-signal state and consists only of noisecomponents. Accordingly, the sum signal SUM shown in FIG. 1 is almostequal to the push-pull signal PP1. The difference signal DIFF is alsoalmost equal to the push-pull signal PP1. Two signals in phase aresupplied to the phase comparator 28, which then determines that thephases of these signals are the same.

Thus, by determining whether the sum and difference signals SUM and DIFFbetween the push-pull signals PP1 and PP2 are in phase or out of phase,it can be determined which of the two land regions 3, 4 the main beam MBis tracing. Consequently, the phase comparator 28 outputs land areadetermination information D indicating which of the two land regions 3,4 the main beam MB is tracing.

Which of the two land regions 3, 4 the main beam MB is tracing can alsobe determined even if the inputs to the subtractor 27 are reversed toprovide opposite phase determination conditions.

The sum signal SUM, which is an output signal from the adder 26, is alsosupplied to the FM demodulator 29, as shown in FIG. 1. The FMdemodulator 29 demodulates a supplied wobble signal to output a biphasecoded address signal.

The biphase demodulator 30 decodes the output signal from the FMdemodulator 29 to obtain address information AD.

As described above, by comparing the phases of the sum and differencesignals SUM and DIFF between the push-pull signals PP1 and PP2 todetermine the mutual phase relationship, which land region the main beamlight MB is tracing can be determined immediately after the beam lightMB has focused on the land area.

In addition, by inputting the sum signal SUM of the push-pull signalsPP1 and PP2 to the demodulating means, the address information AD can beobtained using one set of demodulating means.

Although Embodiment 1 is constructed to obtain the address informationAD from the sum signal SUM, similar effects can be obtained even if itis constructed to obtain the address information AD from the differencesignal DIFF.

Embodiment 2

Embodiment 2 uses the same optical disc device as in Embodiment 1 exceptfor the address demodulating circuit.

The address demodulating circuit according to Embodiment 2 is composedof the split photo detectors 21, 23, the quadrant photo detector 22, thesignal processing means 31, the phase comparator 28, the demodulatingmeans, and a signal selector 32, as shown in FIG. 3. The modulatingmeans is composed of the FM demodulator 29 and the biphase demodulator30.

This address demodulating circuit includes the signal selector 32 thatselects one of the two push-pull signals PP1, PP2 based on the land areadetermination information D outputted from the phase comparator 28. Thepush-pull signal selected by the signal selector 32 reasonably containswobbling information, which is demodulated by the FM demodulator 29 andthe biphase demodulator 30 as in Embodiment 1 to obtain the addressinformation AD from the wobbling information.

According to Embodiment 1, the signal processing means 31 demodulatesthe sum signal SUM obtained by adding the two push-pull signals PP1, PP2together in order to obtain the address information AD, as shown in FIG.1. One of the two push-pull signals PP1, PP2 does not contain thewobbling information and is in a non-signal state, but it actuallycontains noise components. Thus, the sum signal SUM obtained by theadder 26 has its noise level increased by {square root over (2)} timesto degrade the S/N ratio and thus the error rate for the reading of theaddress information (AD), though it does not exceed the correspondingpermissible range.

According to Embodiment 2, however, the signal selector 32 selects anddemodulates one of the push-pull signals PP1, PP2 that contains wobblinginformation, based on the land area determination information D outputfrom the phase comparator 28. Consequently, the S/N ratio or the addressreading error rate is not degraded as in Embodiment 1, and the addressinformation AD can be demodulated appropriately.

As described above, the address information AD can be obtained using oneset of demodulating means, by inputting to the demodulating means,output from the signal selector 32 that selects one of the push-pullsignals PP1, PP2 that contains wobbling information, based on the landarea determination information D from the phase comparator 28.

As described above, the optical disc device signal processing method ofthis invention compares the phases of the sum and difference signalsbetween the push-pull signal obtained from the output from the firstsplit photo detector and the second push-pull signal obtained from theoutput from the second split photo detector in order to determine fromthe mutual phase relationship which land area is reflecting the mainbeam light. Thus, it does not make this determination based on thepresence of address information after the two push-pull signals havebeen demodulated using two sets of demodulating means as in the priorart. As a result, this method is not subjected to processing delay timein the demodulating means, and can determine which land region the mainbeam light is tracing, immediately after the beam light has focused onthe land area.

In addition, the optical disc device of this invention comprises thesignal processing means for detecting the sum and difference signalsbetween the first push-pull signal obtained from output from the firstsplit photo detector and a second push-pull signal obtained from outputfrom the second split photo detector; and the phase comparator forcomparing the phases of the sum and difference signals to determine themutual phase relationship, and uses the determination output from thephase comparator, as the land area determination information. Thus, thisdevice can implement the optical disc device signal processing method ofthis invention.

In addition, by demodulating the sum or difference signal from thesignal processing means or using the signal selector to select anddemodulate one of the two push-pull signals that contains wobblinginformation, based on the determination output from the phasecomparator, this invention eliminates the need to provide two sets ofdemodulating means as in the prior art and requires only one set ofdemodulating means. Therefore, this invention can implement an opticaldisc device using a simple configuration and is very practicallyeffective.

What is claimed is:
 1. A method of processing signals for an opticaldisc device, in which a track format optical disc (5) has two land areas(3, 4) of a double spiral structure on which information is recorded,said land areas being arranged adjacent to each other sandwichingbetween a wobbling groove (1) on which wobble information is recorded bywobbling, an has non-wobbling grooves (2) arranged outside said landareas, the method comprising the steps of: detecting a first reflectedlight obtained by irradiating the land areas; using a first split photodetector (21) disposed at a first prescribed position to detect a secondreflected light obtained by irradiating the wobbling groove (1) or thenon-wobbling groove (2) located adjacent to one side of the land areaproviding the reflected light; using a second split photo detector (23)disposed at a second prescribed position to detect a third reflectedlight obtained by irradiating the wobbling (1) groove or thenon-wobbling groove (2) located adjacent to the other side of the landarea providing the reflected light; and recording or reproducinginformation on or from the land area while executing tracking controlbased on the first, second, or third reflected light or on a combinationof these lights, wherein phases of a sum signal and a difference signalare compared between a first push-pull signal obtained from an outputfrom the first split photo detector (21) and a second push-pull signalobtained from an output from the second split photo detector (23), inorder to determine from the phase relationship obtained between the sumand difference signals which land area (3, 4) is providing said firstreflected light.
 2. An optical disc device, in which a track formatoptical disc (5) has two land areas (3, 4) of a double spiral structureon which information is recorded, said land areas being arrangedadjacent to each other sandwiching therebetween a wobbling groove (1) onwhich wobble information is recorded by wobbling, and has non-wobblinggrooves (2) arranged outside said land areas, said optical disc deviceexecuting: detecting a first reflected light obtained by irradiating theland area; using a first split photo detector (21) disposed at a firstprescribed position to detect a second reflected light obtained byirradiating the wobbling groove (1) or the non-wobbling groove (2)located adjacent to one side of the land area providing the reflectedlight; using a second split photo detector (23) disposed at a secondprescribed position to detect a third reflected light obtained byirradiating the wobbling groove (1) or the non-wobbling groove (2)located adjacent to the other side of the land area providing thereflected light; and recording or reproducing information on or from theland area while executing tracking control based on the first, second,or third reflected light or on a combination of these lights, whereinsaid optical disc device comprises: signal processing means (31) fordetecting a sum signal and a difference signal between a first push-pullsignal obtained from an output from the first split photo detector (21)and a second push-pull signal obtained from an output from the secondsplit photo detector (23); and a phase comparator (28) for comparingphases of the sum and the difference signals to determine a mutual phaserelationship, in order to use a determination output from the phasecomparator as land area determination information.
 3. The optical discdevice according to claim 2, wherein an output signal from the signalprocessing means (31) is demodulated to obtain address information. 4.The optical disc device according to claim 2, further comprising asignal selector that selects between the first push-pull signal and thesecond push-pull signal based on the land area determination informationoutputted from the phase comparator (28), whereby the push-pull signalselected by the signal selector is demodulated to obtain addressinformation.